The present invention relates to improvements in a shift shock reducing apparatus of a continuously variable transmission equipped vehicle.
A continuously variable transmission (CVT) such as a belt type CVT or toroidal type CVT is generally arranged to execute a shift control in a manner such as to obtain a target transmission ratio from a required engine load and a vehicle speed and to adjust an actual transmission ratio (actual CVT ratio) at the target transmission ratio. Therefore, in case that the required engine load is increased according to the increase of a depression of an accelerator pedal to accelerate the vehicle or that the vehicle speed is decreased due to the shortage of the driving force, the target transmission ratio is increased, that is, it is changed to a lower speed side transmission ratio. More particularly, the CVT is downshifted to the increased target transmission ratio. On the other hand, in case of a low-load driving condition such that the required engine load is decreased according to the decrease of the depression of the accelerator pedal or in case of a vehicle speed increasing condition such that the vehicle speed is increased due to excessive driving force, the target transmission ratio is decreased, that is, it is changed to a higher speed side transmission ratio. More particularly, the CVT is upshifted to the decreased target transmission ratio. By this shifting, the engine rotation speed (engine rotation inertia) is changed according to the change of the transmission ratio. When the downshift is executed while increasing the engine rotation speed, the engine torque is lowered by a negative inertia torque as shown by a two-dot chain line in FIG. 9D. This lowering of the engine torque generates shift shocks having a pop-down feeling of the torque such as shown by hatching parts of FIGS. 9E and 9F. Further, when the upshift is executed while decreasing the engine rotation speed, a positive inertia is generated. This positive inertia generates shift shocks having a pop-up feeling of the torque, though not shown in the Figure.
In order to suppress these shift shocks, various apparatuses have been proposed, for example, in Japanese Patent Provisional Publications Nos. 5-99011 and 7-239002. An apparatus disclosed in the former publication is arranged to lower an engine torque when the shifting is started, in order to suppress shift shocks caused by the upshift. Further, an apparatus disclosed in the latter publication is arranged to decrease a rate of change in the transmission ratio (CVT ratio) per time as shown by a two-dot chain line in FIG. 10B to suppress shift shocks as shown by two-dot chain lines in FIGS. 10D, 10E and 10F.
However, these two conventional apparatuses still have problems to be solved, such that it is difficult to satisfactorily suppress shift shocks during the shifting or to execute shift shock reducing process without degrading the drivability of a vehicle.